0 Assigned ID: 511 ----- Attempting Submission 1 (Fri Apr 10 15:33:11 GMT 2015) ----- HST Phase I Proposal 511 (rudnick.hstcyc23.apt) successfully submitted. Receipt: # 511-1 ----- Attempting Submission 2 (Fri Apr 10 18:48:32 GMT 2015) ----- For decades we have known that galaxy clusters had a lower fraction of passive galaxies in the past. However, despite intense study we still do not know how or when passive galaxies became passive and what role the cluster environment plays. Key to making progress in this endeavor is bringing the study of clusters to z>1, where the massive passive galaxies entered their last epoch of star formation. This is just now possible as the number of z>1 clusters is burgeoning, as is the ability to select and study passive galaxies within them, largely thanks to HST observations. We propose to use archival HST imaging of 22 galaxy clusters at z>1 to systematically study how the passive galaxy population in the densest environments has grown over the last 10 billion years. Using photometry that spans the 4000 Ang break at each redshift, we will isolate passive member galaxies and measure their rest-frame optical luminosity and stellar mass functions. We will match clusters with their likely descendants at all redshifts using the predicted growth of their dark matter halos and will constrain the evolution both in the mass functions and luminosity functions. We will use the HST imaging to compute internal stellar mass density, which has been shown to be an excellent predictor of intrinsic quenching. Finally, using models for intrinsic and environmental quenching and merging that we have already developed, we will determine the relative importance of these processes in growing and shaping the passive galaxy population in clusters. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 0 Regular false false false false false SUPPORTED